Tetrahydrofuran is an important organic material which finds application as a versatile solvent medium and as an intermediate for the production of resins and other commercial products such as butyrolactone and succinic acid.
Tetrahydrofuran can be produced by catalytic hydrogenation of maleic anhydride or furan, as is described in patent literature such as U.S. Pat. Nos. 2,772,293; 2,846,449; 3,021,342; and references cited therein.
It is well known that tetrahydrofuran can be produced by a series of reactions starting with the reaction of aqueous formaldehyde and acetylene in the presence of a cuprous acetylide complex to form butynediol. An alkaline material such as the carbonate, bicarbonate or hydroxide of an alkali or alkaline earth metal is commonly added to this reaction to control pH. This alkaline material generally reacts with the formic acid generated in this reaction to form the metal formate. The product of this reaction is then passed to a hydrogenation step where the butynediol is converted to butanediol.
The aqueous product stream from the hydrogenator is then concentrated to form a butanediol feed stream, typically containing, by weight, about 3 percent water, about 95-96 percent butanediol, and about 0.5-2 percent combined high boiling organic tars and alkali metal or alkaline earth metal salts. The butanediol is then converted to tetrahydrofuran using about 10 percent sulfuric acid. This reaction is carried out under temperature conditions which allow recovery of tetrahydrofuran and water overhead from the reactor. At equilibrium the reaction medium in the reactor typically contains about 50-60 percent unconverted butanediol, about 10 percent acid, about 10 percent water, and about 25 percent combined tars and salts. The build-up of tars and salts in the reactor is an undesirable characteristic of this type of process.
There is a need for new and improved commercial processes for the large volume production of tetrahydrofuran. The development of such processes is under active investigation.
Accordingly, it is an object of the present invention to provide a new and efficient method for producing tetrahydrofuran.
It is another object of the present invention to provide a method for converting 3-(5'-alkyl-1',3'-dioxane)propionaldehyde and/or 3-(5'-alkyl-1',3'-dioxane)propanol and/or 4-hydroxybutanal into tetrahydrofuran in high yield.
It is a further object of the present invention to provide a procedure for hydrogenating 3-(5'-methyl-1',3'-dioxane)propionaldehyde which can be integrated as an essential step in a commercially feasible process for converting acrolein into tetrahydrofuran.
Other objects and advantages shall become apparent from the accompanying description and examples.